Mechanical seal

ABSTRACT

In mechanical seals adapted to perform in high temperature environments, fragile gaskets characterized by poor elasticity and conformability are used to perfect a seal between adjacent parts. Gaskets may be made of graphite, carbon, asbestos and/or fiberglass containing material. In order to perfect such a seal, gaskets with a parallelogram cross-section are used. They are expanded radially and their cross-section changed when placed between two parts during assembly.

This is a division of application Ser. No. 837,790 filed Sept. 29, 1977U.S. Pat. No. 4,124,218 Nov. 7, 1978.

BACKGROUND OF THE INVENTION

Mechanical seals are frequently used in high temperature environments toseparate fluids of different kinds. One form of high temperature seal isknown as the bellows-type seal, i.e., a seal in which an expansiblebellows is used. High temperature uses of mechanical seals dictate hightemperature resistant gaskets retained and highly compressed betweenvarious parts by the use of bolts. These are in lieu of the moreconventional rubber O-ring seals. Some of the more common gasketmaterials are those containing carbon, graphite, asbestos and/orfiberglass, i.e., fragile materials characterized by poor elasticity andconformability. In the absence of provisions for high clamping forces,the conventional gasket of such materials is precision formed withgasket surfaces and cross-sections matching the surfaces andcross-sections of their receiving cavities. By their very nature, suchmaterials cannot readily be made to the degree of precision required toprovide a leak-tight fit by close or precision fit alone, so that highclamping forces are required to perfect the seals. As can be readilyunderstood, the known gaskets are relatively expensive because of theirmethod of manufacture and have little ability to seal over even veryslight surface flaws. And the product must be constructed to permit therequisite clamping forces.

THE INVENTION

According to the invention to be hereinafter described, hightemperature, fragile gasket materials are formed with an initialcross-section in the shape of a parallelogram or similar shape, suchthat upon assembly in a gasket cavity and the fitting of the gasketedparts, the gasket is deformed and expands in a radial direction, thusfilling the cavity and insuring a seal between the joined parts. Thegaskets because of their very nature deform and provide the requisiteexpansion in certain directions to fill its cavity with a minimum ofaxial pressure. And when so deformed, such gaskets are tightlycompressed in the area of actual sealing. Thus partially filled areas ofthe gasket cavity, if any, cause less serious problems than wouldotherwise be the case. The normally required bolting of parts to providehigh clamping forces is not generally required; however, if desired, agreater range of expansion can be achieved to compensate for ill fittingparts by the use of the conventional bolting technique.

When securing carbon or other similar high temperature gasket materialsto a metal bellows, space and weight requirements preclude the use ofbolts. The invention herein described permits the use of hightemperature gasket materials with a fairly low initial seating forceduring assembly, and, of course, in a bellows type seal.

THE DRAWINGS

FIG. 1 is a partial longitudinal section through a typical bellows-typemechanical seal according to this invention;

FIG. 2 is an enlarged, partial sectional view showing aparallelogram-sectioned gasket in a cavity before the distortion of thegasket;

FIG. 3 is a view similar to FIG. 2 showing the gasket distorted; and

FIG. 4 is a detail of the bellows ferrule and seal ring connection.

DETAILED DESCRIPTION

Attention is invited to the drawings in which FIG. 1 shows a mechanicalseal assembly, identified as 10 associated with a rotary shaft 12 and aseal flange 14, which comprises a pair of seal rings 16 and 18 havingradially disposed engaging seal faces 20 and 22, respectively.

The seal ring 16 is rotatable with the shaft 12 and abutts a shoulder 24on a sleeve 26 surrounding the shaft 12. In order to urge the seal ring16 against the shoulder 24, there is provided a back-up ring 28 and alocking ring 30, the latter being connected, as by a snap ring 32 to theshaft 12. Two or more adjusting screws 34 received in the locking ringand bearing against the back-up ring 28 force the back-up ring 28 andseal ring 16 against the shoulder 24 and thereby lock it in positionwith a minimum of runout or distortion.

The seal ring 18 is stationary and fixed, as will be described, to theflange 14. The seal ring 18 is surrounded by a metal ferrule 36 in whichit is slip fit, fingers 37 in the ferrule 36 engaging notches 38 in theseal ring 18 to lock them against relative rotation, (see detail of FIG.4). The ring 18 is also notched as at 39 to define, with a radialportion 40 of the ferrule 36, a substantially rectangular cavity 42. Abellows 44, generally constructed of annular elements welded together,is attached at one end, as by welding, to an annular bead 46 on theportion 40 of the ferrule 36. At the other end, the bellows 44 is weldedto an annular bead 48 of a bellows support ring 50 internally screwthreaded with threads 52. The threads 52 mate with screw threads 54 onan annular neck portion 56 of an anti-coking device or anti-sparkbushing 58. The anti-coking bushing 58 is constructed totally orpartially of non-ferrous metal and is received in an annular cavity 60in the flange 14; it surrounds and is spaced from the shaft 12 and thesleeve 26. Anti-static bushings, such as the bushing 58, are generallyprovided around ferrous rotating shafts when flammable or explosiveconditions are expected. The seal assembly of this invention isadaptable for such usages. The ring 50 is notched and defines asubstantially rectangular cavity 62 with the flange 14. The anti-cokingbushing 58 is threadably bored at 64 to receive an adjusting screw 66bearing against the support ring 50.

Passageway 68 is provided in the flange 14 which opens into the cavity60; passageway 70 is provided in the anti-coking bushing 58 which opensat one end into the cavity 60 and at the other end at a locationadjacent the shaft 12 axially of the bellows 44. A quench fluid may beintroduced into the passageway 68 to flow through the passageway 70 andout from the seal between the sleeve 26 and the anti-coking bushing 58.

As is usual, one of the seal rings, as for example ring 18, is mostcommonly made of a carbon material, while the seal ring 16 may be of astellite or faced with a stellite or other hard material.

The cavities 42 and 62 are such to each receive a ring gasket 72,74,respectively, in order to provide a fluid-tight seal between the variousparts.

Attention is now invited to FIGS. 2 and 3. FIGS. 2 and 3 illustrate indetail the seal ring 18 and the bellows 44 with a gasket 72 in the shapeof a parallelogram in the cavity 42 with a loose fit. Upon assembly ofthe various parts and adjustment of the screw 34 the gasket 72 isdistorted, causing it to move radially, generally filling the cavity 42,so that it assumes the appearance, in section, shown in FIG. 3.Thereafter, the spring load from the bellows and unbalanced hydraulicforces from the fluid being sealed clamp the gasket in place. The gasket74 may be similar to the gasket 72. Sufficient pressure can be appliedto distort the gasket 74 from its initial shape by adjustment of the setscrew 66. In experimental use, used, distorted gaskets 72 from thecavity 42 have been used for gaskets 74 because high clamping force isavailable for the latter.

When used for high temperature environments, suitable gasket materialsare selected from the group consisting of carbon, graphite, fiberglassand asbestos containing materials, which fragile materials exhibit poorelasticity and conformability. Preferably, gaskets of this invention aremade from a laminated graphite known as "GRAFOIL" and produced by UnionCarbide Co. As before stated, this invention permits the use of gasketswhich do not require the usual degree of forming to precise shapes noris flange bolting required - there need only be sufficient gasketmaterial to fill the gasket cavity to perfect the seal between partswith sufficient force to distort and radially expand the gasket.

The seal assembly of this invention is usable in applications whereinthere is a desired separation of fluids, as for example in a pump-motorcombination wherein the pump is subjected to product fluid and the motorto a refined, controlled fluid. The latter is customarily used as thequench fluid. The flange 14 may be connected to the pump housing (76 forexample) such that the pump is connected to the shaft at the right, asviewed in the drawings and the motor to the shaft at the left, also asviewed in the drawings. Moreover, the seal of this invention, because ofthe use of a shaft sleeve can be removed, as a unit, for service orreplacement without disassembly of the seal components.

What is claimed is:
 1. A mechanical seal comprising a stationary sealring and a rotatable seal ring, said seal rings having engaging sealfaces;a ferrule surrounding and in contact with the outer surface of oneof said seal rings and having a depending flange; a substantiallyrectangular section, annular cavity defined by a groove in said one ofsaid seal rings and a portion of said ferrule and its flange; and agasket of fragile material characterized by poor elasticity andconformability in said cavity, said gasket having an initialcross-section of a parallelogram and being expanded radially anddeformed to an ultimate cross section matching that of said cavity whenassemblying said ferrule and said one of said seal rings.
 2. Amechanical seal as in claim 1 in which said gasket material is selectedfrom the group consisting of graphite, carbon, asbestos and fiberglasscontaining materials.